In order to prevent counterfeiting, an optical security element with diffraction optical variable image (for example, a hologram, a dynamic diffraction picture, and the like) is widely used in various prints with high security and high value-added, such as bank notes, identification cards, and product packages, and it achieves a good effect. For example, euro bank notes in large denomination adopt is hot stamping patches with diffraction optical variable image, while bank notes in small denomination adopt hot stamping stripes with diffraction optical variable image. The RMB, except the denomination of one yuan, adopts window threads with diffraction optical variable image. Visa, MasterCard and UnionPay cards adopt the hot stamping patches with diffraction optical variable image; and important documents in China such as ID cards, driving licenses, and passports also adopt the anti-counterfeiting technology of diffraction optical variable image. Currently, most of the bank notes, credit cards, passports and the like in the world also adopt the anti-counterfeiting technology of the diffraction optical variable image.
The diffraction optical variable image, under the condition of white light illumination, can reconstruct three-dimensional effect, dynamic change, color change images and the like, and under the condition of laser illumination or by means of other supplementary measures (a decoding plate, a magnifying lens, and the like) can reconstruct a hidden pattern, an encoded pattern, and the like. The former is an anti-counterfeiting feature for public while the latter is anti-counterfeiting feature for professionals and experts. The optical structure of these anti-counterfeiting products is diffraction grating of a surface relief type, and is generally manufactured by transferring the diffraction structure on a base layer through molding process.
The diffraction optical variable image in the prior art can only have parallax in one direction (generally defined as a horizontal direction), and have no parallax in a perpendicular direction (defined as a vertical direction). That is to say, three-dimensional and dynamic effects can only be achieved in the horizontal direction rather than in the vertical direction. This is decided by the optical grating structure of the existing diffraction optical variable image. Due to its strong chromatic dispersion, a clear image can be obtained under the condition of white light illumination, only that parallax in the vertical direction is sacrificed. In addition, the existing diffraction optical variable image reconstructs an image in a direction of ±1 level light, but reconstructs no image in the reflected light/transmission light (0 level) direction.